1. Field of the Invention
The present invention relates to power generation control system and method for an internal combustion engine of a vehicle.
2. Description of Related Art
For example, in a direct fuel injection engine (also referred to as a direct injection engine), which directly injects fuel into cylinders, a combustion mode is changed between a stratified combustion mode and a homogeneous combustion mode based on an operational condition, such as a load of the engine. Also, in a lean-burn engine, a combustion mode is changed between a stoichiometric combustion mode and a lean combustion mode based on an operational condition, such as a load of the engine. In the stoichiometric combustion mode, the air/fuel mixture gas, which is around a theoretical air/fuel ratio, is combusted. In the lean combustion mode, a lean air/fuel mixture is combusted.
Similar to a normal intake port injection engine, which does not change its combustion mode, even in these combustion mode variable engines, a power generator (an alternator), which is driven by a drive force of the engine, is provided. The electric power generated by the power generator is supplied to various electric devices, and the surplus electric power generated by the power generator is stored in a battery. In many cases, the power generation quantity of such a power generator (i.e., the quantity of electric power generated by the power generator) is controlled by controlling the control electric current (field current) of the power generator in a manner that avoids shortage of the electric charge of the battery through monitoring of the battery (see Japanese Unexamined Patent Publication No. 2000-4502 and Japanese Unexamined Patent Publication No. 2001-78365).
As described above, in the combustion mode variable engines, the combustion mode is changed based on the operational condition, such as the load. Thus, when the power generation quantity of the power generator is changed in a load range near a change boundary between the two combustion modes, the load of the engine changes in an amount that corresponds to the change in the drive torque (hereinafter, referred to as power generation toque) of the power generator, so that the combustion mode is changed. Thus, at the time of driving the vehicle at the load range around the boundary between the two combustion modes, the combustion mode may possibly be frequently changed by the change in the power generation torque. The change of the combustion mode is accompanied with the change of the engine torque. Thus, when the combustion mode is frequently changed due to the change of the power generation torque during the driving of the vehicle, the driver of the vehicle may frequently feel the torque change, thereby deteriorating the drive feeling of the driver.